Design Of Stirred Batch Reactor

Presented By: SAQIB RAUF

What is bio-reactor• A bioreactor may refer to any manufactured

or engineered device or system that supports a biologically active environment

• In one case, a bioreactor is a vessel in which a chemical process is carried out which involves organisms or biochemically active substances derived from such organisms. This process can either be aerobic or anaerobic. These bioreactors are commonly cylindrical, ranging in size from litres to cubic metres, and are often made of stainless steel.

Cont..

•A bioreactor may also refer to a device or system meant to grow cells or tissues in the context of cell culture. These devices are being developed for use in tissue engineering or biochemical engineering

Classification of bio-reactors

•On the basis of mode of operation, bioreactor may be classified as

•Batch•Fed batch•continuous•Organisms growing in bioreactors may be•Suspended •Immobilized

WHAT IS FERMENTATION?

Enzymes break down starch into simple sugars, and yeast ferments sugars into ethanol, giving off carbon dioxide gas as a by product. The process has been used since civilization began. Starch is made up of long chains of glucose molecules coiled together. The starch must be broken down into sugars that are only one or two molecules long for the yeast to feed on.

REACTION

305 KC6H12O6 (l)------------------> 2C2H5OH (l) + 2CO2 (g) 180 kPa

∆H0r = -285 kJ /kg C2H5OH

•Reactor Selection•Process Design•Mechanical Design•Heat Calculation•Specification Sheet

REACTOR DESIGN

REF: Chemical Process Engineering Design and Economics By Harry Silla

SELECTION OF REACTOR

Our system is gas-liquid system. We select a batch stirred tank reactor. This is due to the following reasons:

• We need to have the bio mass and molasses in contact with each other for a long time.

•Need to mix the nutrients, bio mass and molasses well together.

•Visited MURREY BREWERY INDUSTRY RAWALPINDI where batch process was taking place.

•Concentration and temperature of the species is uniform through out.

REF: Chemical Process Engineering Design and Economics By Harry Silla

The following table tells us that a stirred batch reactor is common for gas-liquid systems.

SELECTION OF REACTOR

REF: Chemical Process Engineering Design and Economics By Harry Silla

BATCH REACTOR

REF: Chemical Process Engineering Design and Economics By Harry Silla

•Fermenter modeled as a batch reactor.

•Batch reactor consists of an agitator and a jacket around it for cooling purposes.

•Reactants are filled in and allowed to react for a certain period of time without them exiting.

•Jacket consists of agitation nozzles for providing higher turbulence and hence better heat transfer.REF: Chemical Process Engineering Design and Economics By

Harry Silla

BATCH REACTOR

•Fermenter modeled as a batch reactor.

•Batch reactor consists of an agitator and a jacket around it for cooling purposes.

•Reactants are filled in and allowed to react for a certain period of time without them exiting.

•Jacket consists of agitation nozzles for providing higher turbulence and hence better heat transfer.REF: Chemical Process Engineering Design and Economics By

Harry Silla

BATCH REACTOR

•There are 2 fermenters installed in parallel.

•According to a journal, the conversion is 70 % and for that conversion the reaction time is 48 hrs.

•2 fermenters are used because 1 would give us very large dimensions.

BATCH REACTOR

PROCESS DESIGN

PROCESS DESIGNIn sizing of a batch reactor, the following rate equations have to be followed to calculate the reaction time;

REF: Chemical Reaction Engineering By Octave Levenspiel

PROCESS DESIGNThe yeast being used is Saccharomyces cerevisiae. According to an experimental research paper, for a conversion of 70%, the time taken for the batch reaction is 48 hrs. The following equation was then used to calculate the entire batch time.

Where;

tF’ = Time needed for filling.tR = Time taken for reaction.tC’ = Time taken to cool.tE’ = Time taken for emptying and cleaning.tB = Time taken for the entire batch operation.

REF: Chemical Process Engineering Design and Economics By Harry Silla

REF: Journal of Tokyo University of Fisheries, Vol 90, pp. 23-30, 2003

Time required for the entire batch operation:

Charging time (tF’ ): 2 hrs. Cooling time (tC’) : 1.5 hrs. Reaction time (tR): 48 hrs. Emptying and cleaning time (tE’) : 0.5 hrs.

Total time for batch (tB): 2 + 1.5 + 48 + 0.5 = 52 hrs.

REF: Crystalline Chemical Industries

PROCESS DESIGNVolume of Fermenter:

Conversion = 70%.

Reaction Time = 48 hrs.

Batch Time (tB) = 52 hrs.

No. of Fermenters used = 2

Working Pressure of Vessel (P) = 180 kPa

Temperature of Reaction = 32 oC.

pH = 4.8

Mass flow rate in (ml’) = 6700 Kg/hr.

Density of Material in Fermenter (ρ’) = 1200 Kg/m3.

Now;tB = 52 hrs.

Density of Feed (ρ’) = 1200 Kg/m3.

Now;ml’ = 6700 Kg/hr

Therefore;Vr = 6700 x 52

1200 Vr = 290 m3.

REF: Chemical Process Engineering Design and Economics By Harry Silla

VOLUME OF FERMENTER

Now;

We allow 30% of volume of fluid as the free space in the fermenter.

Hence;With 30% allowance;

VT = 1.30 x Vr

= 1.30 x 290= 377 m3.

REF: Chemical Process Engineering Design and Economics By Harry Silla

Dimensions:

H/D = 1.5 VT = Π x (D2/4) x L

= Π x (D2/4) x 1.5D= (3/8)Π x (D3)

VT = 377 m3.

Hence, putting in above equation;

D = 6.8 m.

H = 10 m

Now;

Height of Dished Bottom = 1 m( From Literature)

Therefore;

Total Height = 10 + 1 = 11 m.

MECHANICAL DESIGN

Static Pressure (Ps) = ρ’ x g x H

= (1200 x 9.81 x 10)/1000= 129 kPa.

Total Pressure at base = Ps + P

= 309 kPa.

Maximum allowable pressure = 1.33 (309) = 410 kPa.

MECHANICAL DESIGN

WALL THICKNESSFor the calculation of wall thickness we have to calculate the total pressure which is the sum of static pressure and operating pressure of the fermenter.

REF: Plant Design and Economics for Chemical Engineers Max S. Peters et al.

Wall thickness = P x ri + Cc

SEj – 0.6P

Material = Carbon Steel.Working Stress of Carbon Steel,S = 94408 KN/m2.Joint Efficiency, Ej = 0.85

Internal Radius, ri = 3.4 m

Corrosion allowance = 2mm.

Therefore wall thickness = 0.017 + Cc

= 0.017 + 0.002= 0.019 m = 19 mm.

Therefore outside diameter = Di + 2t = 6.84 m.

WALL THICKNESS

REF: Plant Design and Economics for Chemical Engineers Max S. Peters et al.

REACTOR HEAD

There are three types of heads:

•Ellipsoidal Head.

•Torispherical Head.

•Hemispherical Head.

Ellipsoidal head is used for pressure greater than 150 psi and for less than that pressure we use Torispherical head. That is why we have selected a Torispherical head.

REF: Coulson & Richard Chemical Engineering, Vol 6.

REF: Chemical Process Engineering Design and Economics By Harry Silla

TORISPHERICAL HEAD

= 0.019 + 0.002 = 0.021 m = 21 mm.

REF: Coulson & Richard Chemical Engineering, Vol 6.

REF: Chemical Process Engineering Design and Economics By Harry Silla

MECHANICAL DESIGNAGITATOR DESIGN

Agitator Dimensions are:Impeller Diameter Da = Dt/3 = 2.2 mImpeller Height above Vessel floor E = Da

= 2.2 mLength of Impeller Blade L = Da /4

= 0.6 mWidth of Impeller Blade W = Da /5

= 0.4 mWidth of Baffle J = Dt/10

= 0.68 mNo. of Impellers

= 3No. of Impeller blades = 6Distance between 2 consecutive impellers = 2.2 m

Shape Factors are S1 = Da/Dt = 1/3 S2 = E/Dt = 1/3S3 = L/Da = 0.27 S4 = W/Da = 1/5S5 = J/Dt = 1/10 S6 = H/Dt = 1.5

Tip Velocity = 3 – 6 m/secTip Velocity = 5 m/secTip Velocity = π x Da x NSpeed of Impeller = N = [5/( π x 2.2)] x 60 = 44 RPM REF: Unit Processes in Chemical Engineering By Mccabe, Smith &

Harriot

REF: Heuristics in Chemical Engineering Edited for On-Line Use by G. J. Suppes, 2002

Power no (Np )= 6.

Shaft RPM (N)= 44 RPM = 0.7 rev/sec

Power = (Np x N3 x Da5 x ρ)/gc = 52 hp.

Now,

Assuming the impeller is 85 % efficient:

Actual Power required = 52/0.85 = 60 hp.

POWER REQUIREMENT

No. of baffles = 4.

Width of one baffle = Dt / 10 = 0.68 m.

Height of baffle = 10 m.

BAFFLE DESIGN

VISUAL DISPLAY OF AGITATOR WITH DIMENSIONS

VISUAL DISPLAY OF FERMENTER WITH DIMENSIONS

FRONT VIEW

VISUAL DISPLAY OF FERMENTER WITH DIMENSIONS

TOP VIEW

6.84 m

2.2 m

0.68 m

6.80 m

Width of Baffle

Agitator

Cooling Jacket

Cooling fluid used = Cooling Water.

Cooling Jacket area available (A) = 17 m2

This area is obtained from Table 7.3 in “ Chemical Process Engineering Design and Economics by Harry Silla”

CW inlet temp = 20 oCCW outlet temp = 28 oC

Approaches;

• ΔT1= 32 – 20 = 12 0C

• ΔT2= 32 – 28 = 4 0C

LMTD = 7.3 0C = 7.3 0K

HEAT TRANSFER CALCULATION

REF: Chemical Process Engineering Design and Economics By Harry Silla

Heat of Reaction;Q = ∆Hr = 1.1 x 106 kJ/hr Design Overall Coefficient = UD = 170 W/ m2. 0K

Now; Heat Removable by Jacket;Qj = UD x A x LMTD = 23579 W = 8.5 x 107 kJ/hr

Since the heat of reaction (1.1 x 106 kJ/hr) < heat removable by jacket (8.5 x 107 kJ/hr )Our design for a cooling jacket is justified in comparison with a cooling coil.

Now Cooling water Flow rate can be calculated as: Heat to be removed from reactor = 1.1 x 106 kJ/hrMass flow rate of water = Q/( CpΔTM) = 33 Tons/hr

HEAT TRANSFER CALCULATION

REF: Chemical Process Engineering Design and Economics By Harry Silla

SPECIFICATION SHEET

Identification

Item Fermenter

Item Name R-101

No. Required 8

Function Production of Industrial Alcohol by Fermentation

Operation Batch

Type Jacketed, Stirred Tank Reactor

Volume 377 m3

Height 10 m

Diameter 6.8 m

Temperature 32oC

Working Pressure 1.8 atm

Batch Time 52 hrs

Height to Diameter Ratio 1.5

Type of Head Torispherical

Depth of Dished Bottom 1 m

Wall Thickness 0.019 m

Head Thickness 0.021 m

No. of Baffles 4

Width of Baffle 0.68 m

Height of Baffle 10 m

Material of Construction of Fermenter Carbon Steel

Identification

Item Agitator

Type Three 6-bladed Flat Turbine

Number of Blades 6

Impeller Diameter 2.2 m

Length of Blade 0.6 m

Width of Blade 0.4 m

Impeller Above Vessel Floor 2.2 m

Speed of Impeller 44 RPM

Power Required 60 hp

Identification

Item Cooling Jacket

Fluid Handled Cooling Water

Inlet Temperature 20oC

Outlet Temperature 28oC

Flow Rate 33 Tons/hr.

Heat Transfer Area 17 m2

UD 30 BTU/hr.ft2.oF

RD 0.001 hr.ft2.oF/BTU